Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
From the previous discussion regarding the relevance of specific time area, the numerical
level for the intake in question as a function of bmep is given by Eq. 6.1.9 and repeated here
as:
bmep + 1.528
A svi = — s / m (6.4.5)
When the target requirement of bmep for a given swept volume, Vsv, at an engine speed,
rpm, is declared, there is available a direct solution for the design of the entire device. From
Eq. 6.1.12:
2>ede
Specific time area, Asvi = ^ s s/m (6.4.6)
6Vsvrpm
If you glance ahead at Fig. 6.29, the data listed in the upper left-hand side of that figure
contain all of the relevant input data for the calculation, as exhibited in Eqs. 6.4.1 to 6.4.6. It
is seen that the unknown data value which emerges from the calculation is the value of the
outer port edge radius, rmax. This is the most convenient method of solution. Eqs. 6.4.1-6.4.6
are combined, estimates are made of all data but rmax, and the result is a direct solution for
rmax. This is not as difficult as it might appear, for disc valve timings are not subject to great
variations from the lowest to the highest specific power output level. For example, the timing
events, 0dVo an( ^ 9dvc> would be at 150 and 65 for a small scooter engine and at 140 and 80,
respectively, for a racing engine. For completeness, the actual solution route for the determination
of rmax and the carbureter flow diameter (from Fig. 5.5), dtv, is given below:
1 Ad6 = 6AsviVsvrpm (6.4.7)
fAdO
A max = ~ — (6.4.8)
b max ~ ^p
360 CcAmax + rp 2 (4 - it))
r max = J " + r min (6.4.9)
d = 4C c A max (64 10)
V n
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